While in the past several proposals have been made providing a rotatable antenna in a microwave heating apparatus, few products have been in fact provided with such an antenna. To date no commercial products which have such a rotatable antenna have been marketed in Japan or in other countries.
In a typical microwave heating apparatus which has been proposed heretofore, there is provided a bent antenna having the inner end connected by a pin to a driving shaft within a wave guide, and the driving shaft is in turn connected to a driving gear by a pin and is also mounted in a bearing in the wall of the wave guide. In this structure the inner end of the antenna and the driving shaft may not be properly aligned and the tolerances at the various bearings and connections may be such that taken together they permit the position of the outer end of the antenna to be at different distances from the heating chamber wall during antenna rotation, thereby causing uneven distribution of the radiation.